Tried this event today. He got 90% of my raid with a DT or something. So I Feign Death and failed the event. He depopped and I rezed everyone back in.
He then repoped however, this time without the Sacrificial Akhevan. And the event was still running. Got an emote that said Jantarx begin to weave a powerful enchantment that fulls you with immense fear!.
In a few min a second Jantarx spawned with the Sacrificial Akhevan. The Akhevan were already active and started sending the Red and Black essences. One of the Jantarx was absorbing them however, neither Jantarx were active. I could stand next to them as if the event had not started.
Tried this twice and the same thing happens. Assuming that if you were successful on the first attempt it would work fine. =)